What's the shortcut for return to previous 3d viewport scene?
I don't think you can save user perspective locations unless you have a Camera in your scene, in which case you could position the camera to your desired perspective and press "Num 0" to return to that position. 

It might also help to enable "Lock Camera to View", as you could easily adjust the perspective like you would normally in the 3D view. If you switched to any other perspective hotkey, you could just hit Num-0 and go back to your previous view.

Hope that helps, feel free to ask any questions.